Research On Corrosion Wear Properties And Mechanism Of Bainite Wheel And Rail Steel

In high-temperature and high-humidity environments such as tunnels,cross-river bridges,and coastal areas,wheel and rail will suffer from more severe corrosion and wear because of their interaction,resulting in higher cost and possible security problem.It is hard for present pealitic wheel and rail steels to meet the railway development with higher speed and heavier load and novel bainitic steels with excellent general properites have been a promising alternative.However,there is little systematical studies on corrosion and wear performance of bainitic rail and wheel.Therefore,in order to study the influence of misrostructure and alloy elements addition on corrosion as well as wear and provide guidance for related bainitic steels'development,three steels named 1#,2#and 3#through adding Cr and?or?Cu elements were designed based on present Mn-Si-Cr bainitic rail and wheel steels.Their continuous cooling transformation?CCT?and isothermal transformation?TTT?curves were measured.After heat treatment by isothermal quenching?370°C and 400°C?and tempering,the periodic soakage corrosion tests and corrosion-wear tests were made for as-treated samples and present bainitic and pealitic rail and wheel steels.Main results are as followings:1.effect of microstructure on corrosion and wear:?1?.Bainitic and pealitic rail and wheel steels show similar corrosion rate trend.With corrosion time increases,the rate rises at first and then decrease followed by a stable value.Relatively,pearlitic rail and wheel steels demonstrate larger corrosion weight loss,higher average corrosion rate and more and bigger corrosion pits.?2?.Corrosion and corrison-wear resistance of appropriate baintic microstructure are superior to that of pearlitics and bainitic rail and wheel steels have smaller corrosion-wear interaction.2.Effect of heat treatment process on corrosion and wear performance?1?.The trend of microstructure change for three designed steels are similar during isothermal quenching and tempering treatment.There exist mainly lath bainite in the microstructure at 370°C.When isothermal temperature increased from 370°C to400°C,the microstructure is majorly composed of granular bainite.?2?.Corrosion resistance of microstructures mainly of lath bainite is superior to that of mainly granular bainite.After 400°C isothermal treatment,three steels mainly composed of granulare bainite show larger corrosion weight loss,higher average corrosion rate and more and bigger corrosion pits.While aftrer 370°C isothermal treatment,three steels mainly composed of lath bainite have less rust holes and cracks,better substrate protection and corrosion performance.Generally,the rate for three steels rises at first and then decrease followed by a stable value with corrosion time increases.3.Influence of Cu and Cr additon on corrosion and abrasion performance:?1?.The corrosion resistance sequence for as-treated three steels is 2#?Cu+Cr?best,3#?Cr?medium and 1#?Cu?lowest.The corrosion weight loss and average corrosion rate rank by 1#?Cu?>3#?Cr?>2#?Cu+Cr?,and number and size of corrosion pits by 1#?Cu?>3#?Cr?>2#?Cu+Cr?on both 370°C and 400°C isothermal treatment condition.?2?.The addition of element Cu and Cr could improve rust layer density and protect base material.Both of them enrich in inner rust layer and rust layer density rank by 2#?Cu+Cr?>3#?Cr?>1#?Cu?.?3?.Rust layer is mainly composed of?-Fe OOH,?-Fe OOH,?-Fe OOH and Fe₃O_4.Cu and Cr is good to the formation of stable,dense?-Fe OOH with strong adhesion ability and increase the proportion of?-Fe OOH in the layer.This effect could improve stability and hinder ion permeability,resulting in higher corrosion resistance.?4?.Element Cu and Cr addition leads to higher self-corrosion potential,reduced corrosion tendency,lager polarization resistance,lower current density and corresponding reduced corrosion rate.The rank of self-corrosion potential and polarization resistance is 2#?Cu+Cr?>3#?Cr?>1#?Cu?and correspondingly,the sequence of current density is 1#?Cu?>3#?Cr?>2#?Cu+Cr?.?5?.The addition of Cu and Cr is beneficial for corrosion resistance.Hard second phase formation could decrease wear loss and lower interaction between corrosion and wear,resulting in higer corrosion-wear resistance.The wear weight loss of above three steels show small difference.While the wight loss for all as-treated samples are 1#?Cu?>3#?Cr?>2#?Cu+Cr?.